Underwater booster



FIG. 1 is a perspective view of an underwater booster showing the new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The dashed broken lines in the drawings represent portions of the underwater booster that form no part of the claimed design. 

CLAIM The ornamental design for an underwater booster, as shown and described. 